Ovarian cancer (OVCA) is the most lethal of the gynecological malignancies and chemoresistance presents a major hurdle for successful treatment. The mechanism involved in the regulation of chemo- sensitivity is not completely known. The presence of gonadotropin releasing hormones (GnRHs) and their receptors (GnRHRs) in human ovarian surface epithelium raises the possible existence of an autocrine regulatory loop in OVCA and that this system is involved in cisplatin (CDDP)-induced apoptosis. We hypothesize that GnRHs and GnRHRs are important in the control of chemosensitivity and that their dysregulation may confer chemoresistance in OVCA. The objective of our study is to examine the expression and the role of GnRH and its receptor in the regulation of CDDP sensitivity in OVCA, using pairs of chemo-sensitive and chemoresistant human OVCA cell lines with same genetic background and established p53 and Akt status. sIRNA, dominant negatives (DN) and sense cDNA will be used. In Aim 1, regulation of GnRH and GnRHR expression in chemosensitlve (OV2008 and A2780) and chemoresistant (CI 3* and A2780cp) cells treated with CDDP will be determined by RIA, immunocytochemistry, Western blotting and qRT-PCR. Use of p53 mutant cell line will delineate if p53 is involved in CDDP-induced GnRH-mediated apoptosis. In Aim 2, the functionality of endogenous GnRHs and GnRHRs will be assessed by determining if (a) knockdown of GnRH and their receptors in chemosensitlve OVCA cells confer resistance in these cells to CDDP (decreased apoptosis);(b) forced expression of GnRH receptors and/or addition of exogenous GnRH would sensitize chemoresistant OVCA cells to CDDP (increased apoptosis). In Aim 3, we will determine the mechanism of dysregulation of the GnRH system in chemoresistance, by investigating Ca++ signaling and apoptotic response of both sensitive and resistant OVCA cells to CDDP with/without GnRH treatment. We will determine the role of p53 and Akt in this regulation in OVCA cell lines with wild type and mutant p53, p53 gene silencing and reconstitution, expression of constitutively activated as well as DN-Akt. This study will improve the understanding of the molecular mechanism of chemoresistance in ovarian cancer and offer new insight in the development of novel therapeutic strategies for chemoresistant ovarian cancer. PUBLICH HEALTH RELEVANCE: Chemoresistance is a major hurdle for successful ovarian cancer treatment. This study will improve the understanding of chemoresistance in ovarian cancer and offer new insight in the development of novel therapeutic strategies for ovarian cancer.